Multi‐Material 3D Printing of Functionally Graded Hierarchical Soft–Hard Composites

Abstract

Hard biological tissues (e.g., nacre and bone) have evolved for millions of years, enabling them to overcome the conflict between different mechanical properties. The key to their success lies in the combination of limited material ingredients (i.e., hard and soft constituents) and mechanistic ingredients (e.g., functional gradients and building block hierarchical organization). However, the contribution of each material and mechanistic ingredient is still unknown, hindering the development of efficient synthetic composites. Quantitative and systematic studies of hard–soft composites are required to unravel every factor's role in properties outcome. Herein, a voxel‐by‐voxel multi‐material 3D printing technique is used to design and additively manufacture different groups of hard–soft composites. Several combinations of gradients, multilevel hierarchies, and brick‐and‐mortar arrangements are created. Single‐edge notched fracture specimens are mechanically tested and computationally simulated using extended finite element method (XFEM). It is found that functional gradients alone are not sufficient to improve fracture properties. However, up to twice the fracture energy of the hard face is observed when combining functional gradients with hierarchical designs, significantly increasing composite properties. Microscopic analysis, digital image correlation, and strain distributions predicted with XFEM are used to discuss the mechanisms responsible for the observed behaviors.

Study on Chemical Graft Structure Modification and Mechanical Properties of Photocured Polyimide

“…The curing depth of light curing is mainly related to the photosensitivity of resin. At present, most researchers use the Jacobs equation to describe the curing depth: 3 , 6 , 11 , 14 , 46 …”

“…Many researchers are also developing novel materials for specific applications, such as chitosan hydrogels with growth and biocompatibility for biomedical applications, 10 − 13 high-performance isocyanates for space vehicles, and aerospace to automotive and electronics industries, 8 and functionally graded composite materials with hard and soft layers. 14 But the photocurable resins that these researchers have developed for the specific applications still do not combine many properties, into a single system. Recently, many researchers have focused their attention on a special functional material, polyimide, because it is one of the best organic polymer materials with comprehensive performance, and the research, development, and utilization of polyimide has led to it being listed as the most promising project in the 21st century.…”

ITIL: Interlaced Topologically Interlocking Lattice for continuous dual-material extrusion

“…Besides visual attributes, multi-material systems can be used to create parts with graded material properties, by generating composite structures with varying densities of soft and hard materials [10]. Finetuning the small-scale geometry in which such materials are deposited can give a more sophisticated control over the induced material properties, [11,12] and adjusting the small-scale geometry throughout the product on a meso scale can increase the performance of the product even more [13].…”

“…Combining the above we obtain the constrained optimization problem given by Eqs. ( 5) and (12). The √ 3 in Eqs.…”

“…Using the formulae of the constrained optimization problem one can find the maximum force and thus the maximum stress of any design; we can rewrite each of the mechanical constraints Eqs. (10) to (12) to give a formula for 𝐹 and the lowest value of those formulae will give the active failure mode for a given design. The resulting response surfaces are shown in Fig.…”